The present invention pertains to a respirator that has an integrally-disposed filter element in its mask body and that has an impactor element associated with its exhalation valve. The impactor element allows the respirator to remove particulate contaminants from the exhale flow stream.
Filtering face masks are typically worn over a person""s breathing passages for two common purposes: (1) to prevent contaminants from entering the wearer""s respiratory system; and (2) to protect other persons or items from being exposed to pathogens and other contaminants expelled by the wearer. In the first situation, the face mask is worn in an environment where the air contains substances that are harmful to the wearerxe2x80x94for example, in an auto body shop. In the second situation, the face mask is worn in an environment where there is a high risk of infection or contamination to another person or itemxe2x80x94for example, in an operating room or in a clean room.
Face masks that have been certified to meet certain standards established by the National Institute for Occupational Safety and Heath (generally known as NIOSH) are commonly referred to as xe2x80x9crespiratorsxe2x80x9d; whereas masks that have been designed primarily with the second scenario in mindxe2x80x94namely, to protect other persons and itemsxe2x80x94are generally referred to as xe2x80x9cface masksxe2x80x9d or simply xe2x80x9cmasksxe2x80x9d.
A surgical mask is a good example of a face mask that frequently does not qualify as a respirator. Surgical masks are typically loose-fitting face masks that are designed primarily to protect others from contaminants that are exhaled by a doctor or other medical person. Substances that are expelled from a wearer""s mouth are commonly in the form of an aerosol, which is a suspension of fine solids and/or liquid particles in gas. Surgical masks are capable of removing these particles despite being loosely fitted to the wearer""s face. U.S. Pat. No. 3,613,678 to Mayhew discloses an example of a loose fitting surgical mask.
Loose-fitting masks, typically do not possess an exhalation valve to purge exhaled air from the mask interior. The loose-fitting aspect allows exhaled air to easily escape from the mask""s sidesxe2x80x94known as blow byxe2x80x94so that the wearer does not feel discomfort, particularly when breathing heavily. Because these masks are loose fitting, however, they may not fully protect the wearer from inhaling contaminants or from being exposed to fluid splashes. In view of the various contaminants that are present in hospitals and the many pathogens that exist in body fluids, the loose-fitting feature is a notable drawback for loose-fitting surgical masks.
Some tightly-fitting face masks have a porous mask body that is shaped and adapted to filter inhaled air. The filter material is commonly integrally-disposed in the mask body and is made from electrically-charged melt-blown microfibers. These masks are commonly referred to as respirators and often possess an exhalation valve that opens under increased internal air pressure when the wearer exhalesxe2x80x94see, for example, U.S. Pat. No. 4,827,924 to Japuntich. Examples of other respirators that possess exhalation valves are shown in U.S. Pat. Nos. 5,509,436 and 5,325,892 to Japuntich et. al., U.S. Pat. No. 4,537,189 to Vicenzi, U.S. Pat. No. 4,934,362 to Braun, and U.S. Pat. No. 5,505,197 to Scholey.
Known tightly-fitting respirators that possess an exhalation valve can prevent the wearer from directly inhaling harmful particles, but the masks have limitations when it comes to protecting other persons or things from being exposed to contaminants expelled by the wearer. When a wearer exhales, the exhalation valve is open to the ambient air, and this temporary opening provides a conduit from the wearer""s mouth and nose to the mask exterior. The temporary opening can allow aerosol particles generated by the wearer to pass from the mask interior to the outside. Aerosol particles, such as saliva, mucous, blood, and sweat, are typically generated when the wearer sneezes, coughs, laughs, or speaks. Although sneezing and coughing tend to be avoided in environments such as an operating roomxe2x80x94speech, a vital communication tool, is necessary for the efficient and proper functioning of the surgical team. Saliva particles are laden with bacteria. Unfortunately, aerosol particles that are generated by speaking can possibly lead to infection of a patient or contamination of a precision part.
The particles are made when saliva coated surfaces separate and bubble in response to the air pressure behind them, which commonly happens when the tongue leaves the roof of the mouth when pronouncing of the xe2x80x9ctxe2x80x9d consonant or when the lips separate while pronouncing the xe2x80x9cpxe2x80x9d consonant. Particles may also be produced by the bursting of saliva bubbles and strings near the teeth during sneezing or during pronunciation of such sounds as xe2x80x9cchaxe2x80x9d or xe2x80x9csssxe2x80x9d. These particles are generally formed under great pressures and can have projectile velocities greater than the air speed of normal human breath.
Mouth-produced particles have a great range in size, the smallest of which may average about 3 to 4 micrometers in diameter. The projectile particles, however, which leave the mouth and travel to a nearby third party, are generally larger, probably 15 micrometers or greater.
The settling rates of these airborne particles also affect their deposition on a nearby third party, such as a patient. Because particles that are less than 5 micrometers tend to settle at a rate of less than about 0.001 m/s, they are the equivalent of a floating suspension in the air.
Respirators that employ exhalation valves currently are not recommended for use in the medical field because the open conduit that the exhalation valve temporarily provides is viewed as hazardous. See, e.g., Guidelines for Preventing the Transmission of Mycobacterium Tuberculosis in Health Care Facilities, MORBIDITY AND MORTALITY WEEKLY REPORT, U.S. Dept. of Health and Human Services, v. 43, n. RR-13, pp. 34 and 98 (Oct. 28, 1994). The Association of Operating Room Nurses has recommended that masks be 95 percent efficient in retaining expelled viable particles. Proposed Recommended Practice for OR Wearing Apparel, AORN JOURNAL, v. 33, n. 1, pp. 100-104, 1 01 (January 1981); see also D. Vesley et al., Clinical Implications of Surgical Mask Retention Efficiencies for Viable and Total Particles, INFECTIONS IN SURGERY, pp. 531-536, 533 (July 1983). This recommendation was published in the early 1980s, and since that time, the standards for retaining particles have increased. Some organisms, such as those that cause tuberculosis, are so highly toxic that any decrease in the number of contaminants that are expelled is highly desired.
Respirators have been produced, which are capable of protecting both the wearer and nearby persons or objects from contamination. See, for example, U.S. Pat. No. 5,307,706 to Kronzer, U.S. Pat. No. 4,807,619 to Dyrud, and U.S. Pat. No. 4,536,440 to Berg. Commercially-available products include the 1860(trademark) and 8210(trademark) brand masks sold by 3M. Although these respirators are relatively tightly-fitting to prevent gases and liquid contaminants from entering and exiting the interior of the mask at its perimeter, the respirators commonly lack an exhalation valve that allows exhaled air to be quickly purged from the mask interior. Thus, known respirators can remove contaminants from the inhale and exhale flow streams and can provide splash-fluid protection, but they are generally unable to maximize wearer comfort. And when an exhalation valve is placed on a respirator to provide improved comfort, the mask encounters the drawback of allowing contaminants from the mask interior to enter the surrounding environment.
In view of the above, a respirator is needed, which can (i) prevent contaminants from passing from the wearer to the ambient air; (ii) prevent contaminants from passing from the ambient air to the wearer; (iii) prevent splash-fluids from entering the mask interior; and (iv) allow warm, humid, high CO2-content air to be quickly purged from the mask""s interior.
This invention provides such a respirator, which respirator in brief summary comprises: (a) a mask body that defines an interior gas space and an exterior gas space, the mask body comprising an integrally-disposed inhale filter layer for filtering inhaled air that passes through the mask body; (b) an exhalation valve disposed on the mask body, the exhalation valve having a valve diaphragm and at least one orifice, the valve diaphragm and the orifice being constructed and arranged to allow an exhale flow stream to pass from the interior gas space; to the exterior gas space; and (c) an impactor element that is disposed on the exhalation valve in the exhale flow stream; wherein the exhalation valve and impactor element provide the respirator with a ratio of Zn/Dj of less than about 5.
The invention has an impactor element that can prevent particles in the exhale flow stream from passing from the mask""s interior gas space to the exterior gas space. The impactor element is associated with the respirator such that the ratio Zn/Dj is less than about 5. The use of an impactor element with an exhalation valve allows the respirator to be particularly beneficial for use in surgical procedures and for use in clean rooms. The inventive respirator may remove at least 95 percent, preferably at least 99 percent, of any suspended particles from the exhale flow stream. Further, the impactor element can prevent splash fluids from entering the interior gas space by providing a xe2x80x9cno-line-of-sightxe2x80x9d from the exterior gas space to the interior gas space. That is, the impactor element can be constructed to obstruct the view of the open orifice when the valve diaphragm is open during an exhalation. Unlike some previously-known face masks, the invention can be in the form of a tightly-fitting mask that provides good protection from airborne particles and from splash fluids. And because the inventive respirator possesses an exhalation valve, it can furnish the wearer with good comfort by being able to quickly purge warm, humid, high-CO2-content air from the mask interior. In short, the invention is able to provide the wearer with a clean air source and protection from splash fluids, while at the same time make the mask comfortable to wear and prevent potentially-harmful particles from passing to the ambient environment.
In reference to the invention, the following terms are defined as set forth below:
xe2x80x9caerosolxe2x80x9d means a gas that contains suspended particles in solid and/or liquid form;
xe2x80x9cclean airxe2x80x9d means a volume of air that has been filtered to remove particles and/or other contaminants;
xe2x80x9ccontaminantsxe2x80x9d mean particles and/or other substances that generally may not be considered to be particles (e.g., organic vapors, et cetera) but which may be suspended in air, including air in an exhale flow stream;
xe2x80x9cexhalation valvexe2x80x9d means a valve designed for use on a respirator to open in response to pressure from exhaled air and to remain closed between breaths and when a wearer inhales;
xe2x80x9cexhaled airxe2x80x9d is air that is exhaled by a person;
xe2x80x9cexhale flow streamxe2x80x9d means the stream of air that passes through an orifice of an exhalation valve;
xe2x80x9ctexterior gas spacexe2x80x9d means the ambient atmospheric air space into which exhaled gas enters after passing significantly beyond the exhalation valve and an impactor element;
xe2x80x9cimpactor elementxe2x80x9d means a substantially fluid impermeable structure that diverts the exhale flow stream from its initial path to remove a significant amount of suspended particles from the flow stream as a result of the flow stream diversion;
xe2x80x9cinhale filter elementxe2x80x9d means a porous structure through which inhaled air passes before being inhaled by the wearer so that contaminants and/or particles can be removed from the air;
xe2x80x9cintegralxe2x80x9d and xe2x80x9cintegrally-disposedxe2x80x9d mean the filter element is not separably removable from the mask body without causing significant structural damage to the mask body;
xe2x80x9cinterior gas spacexe2x80x9d means the space into which clean air enters before being inhaled by the wearer and into which exhaled air passes before passing through the exhalation valve""s orifice;
xe2x80x9cmask bodyxe2x80x9d means a structure that can fit at least over the nose and mouth of a person and that helps define an interior gas space separated from an exterior gas space;
xe2x80x9cparticlesxe2x80x9d mean any liquid and/or solid substance that is capable of being suspended in air, for example, pathogens, bacteria, viruses, mucous, saliva, blood, etc.;
xe2x80x9crespiratorxe2x80x9d means a mask that supplies clean air to the wearer through a mask body that covers at least the nose and mouth of a wearer and when worn seals snugly to the face to ensure that inhaled air passes through a filter element;
xe2x80x9cvalve coverxe2x80x9d means a structure that is provided over the exhalation valve to protect the valve against damage and/or distortion;
xe2x80x9cvalve diaphragmxe2x80x9d means a moveable structure on a valve, such as a flap, that provides a generally air tight seal during inhalation and that opens during exhalation; and
xe2x80x9cZn/Djxe2x80x9d or xe2x80x9cZn:Djxe2x80x9d means the ratio of the distance between the valve opening and the impactor element (Zn) to the exhalation valve opening height (Dj) (see FIG. 10 and its discussion).